When there are more animals or plants of a particular species than there are of related species, then the first species is called common.
(物种) 常见的 Ear infections are common in preschool children. 耳朵感染在学前儿童中很常见。
A common is an area of grassy land, usually in or near a village or small town, where the public is allowed to go.
公共草地 We went for a walk on the common. 我们在公地上散步。